Optical sensitisation of inorganic photoconductors

ABSTRACT

AN IMPROVED PHOTOCONDUCTIVE MATERIAL FOR USE IN PHOTOCONDUCTIVE RECORDING ELEMENTS IS OBTAINED BY TREATING A CONVENTIONAL INORGANIC METALLIC PHOTOCONDUCTIVE COMPOUND WITH A SMALL AMOUNT OF AN ORGANIC CHELATING AGENT WHICH IS ADAPTED TO FORM WITH THE METALLIC IONS OF THE PHOTOCONDUCTIVE COMPOUND A COLORED CHELATE OF INCREASED LIGHT-SENSITIVITY RELATIVE TO THE UNTREATED PHOTOCONDUCTIVE COMPOUND. A PREFERRED AMOUNT OF THE CHELATING COMPOUND IS 0.001-0.5% BY WEIGHT OF THE PHOTOCONDUCTIVE COMPOUND. A VARIETY OF SUITABLE ORGANIC CHELATING AGENTS ARE DISCLOSED.

U.S. Cl. 961.7 6 Claims ABSTRACT OF THE DISCLOSURE An improved photoconductive material for use in photoconductive recording elements is obtained by treating a conventional inorganic metallic photoconductive compound with a small amount of an organic chelating agent which is adapted to form with the metallic ions of the photoconductive compound a colored chelate of increased light-sensitivity relative to the untreated photoconductive compound. A preferred amount of the chelating compound is 0.00l-0.5% by weight of the photoconductive compound. A variety of suitable organic chelating agents are disclosed.

This application is a continuation of Ser. No. 542,753 filed Apr. 14, 1966, now abandoned.

The present invention relates to a recording and reproduction material containing a spectrally sensitized inorganic photoconductive substance and a process for sensitizing said substance.

As inorganic photoconductive substances are known eg the oxides, sulphides and selenides of zinc, cadmium, mercury, antimony, bismuth and lead.

The sensitizing agents for inorganic photoconductive substances may be inorganic as Well as organic. For instance, -for the sensitization of photoconductive zinc oxide mercury sulphide, lead oxide and lead iodide have been proposed as well as organic dyestulfs such as triphenyl methane derivatives, sulphone phthaleins and cyanine dyes of various kinds.

We now have found that an organic compound which can complex a metal ion of the type provided by the inorganic photoconductor and forms a coloured chelate therewith possesses optical sensitizing properties for said inorganic photoconductor.

More particularly several classes of chelating compounds have been found that optically sensitize photoconductive zinc oxide in the absorption range of the formed chelate.

A first class of such compounds is represented by the following general Formula I:

s a s wherein:

R represents a hydrogen atom, an alkyl radical e.g. an alkyl radical having from 1 to carbon atoms, and

Each of Z and Z represents the atoms necessary for completing a nitrogen-containing five or six-membered ring. Said five or six-membered ring may contain in addition to the nitrogen atom one or more hetero atoms e.g. oxygen, nitrogen, selenium, or sulphur atoms to form a known heterocyclic ring such as those of the thiazole series (e.g. thiazole, 4-methylthiazole, 4-methyl-5-carbethoxythiazole, 4e'phenylthiazole, S-methylthiazole', 5- phenylthiazole, 4-(p-tolyl)thiazole, 4-(p-bromopheny1)- United States Patent 0 3,600,155 Patented Aug. 17, 1971 thiazole, 4,5-dimethylthiazole, 4,5-diphenylthiazole, 4-(2- thienyl)-thiazole, 4-(m-nitrophenyl)thiazole), those of the benzothiazole series (e.g. benzothiazole, 4-chlorobenzothiazole, S-chlorobenzothiazole, 6-chlorobenzothia zole, 7-chlorobenzothiazole, 4-methylbenzothiazole, 5- methylbenzothiazole, 6 methylbenzothiazole, 5 bromobenzothiazole, 6-bromobenzothiazole, 6-sulfonic acid benzothiazole, 4-phenylbenzothiazole, S-phenylbenzothiazole, 4-methoxybenzothiazole, S-methoxybenzothiazole, 6-methoxybenzothiazole, 5 iodobenzothiazole, 6 iodobenzothiazole, 4-ethoxybenzothiazole, S-ethoxybenzothiazole, 4,5,6,7-tetrahyd-robenzothiazole, 5,6-dimethoxybe'nzothiazole, 5,6-dioxymethylenebenzothiazole, S-hydroxybenzothiazole, 6-hydroxybenzothiazole, 5,6-dimethylbenzothiazole), those of the naphthothiazole series (e.g. naphtho- [2,1-d]thiazole, naphtho[1,2-d]thiazole, 5-methoxynaphtho[l,2 d]thiazole, 5-ethoxynaphtho[1,2 d]thiazole, 8- methoxynaphtho[2,l d]thiazole, 7-methoxynaphtho[2,ld]thiazole), those of the thionaphtheno[7,6-d]thiazole series (e.g. 7 methoxythionaphtheno[7,6 d]thiazole), those of the thiadiazole series (e.g. 4-phenylthiadiazole), those of the oxazole series (e.g. 4-methyloxazole, 5- methyloxazole, 4-phenyloxazole, 4,5-dipheny1oxazole, 4- ethyloxazole, 4,5-dimethyloxazole, 5-phenyloxazole, those of the benzoxazole series (e.g. benzoxazole, 5-chlorobenzoxazole, S-methylbenzoxazole, S-phenylbenzoxazole, 6 methylbenzoxazole, 5,6 dimethylbenzoxazole, 4,6-dimethylbenzoxazole, S-methoxybenzoxazole, 6-methoxybenzoxazole, 5 -hydroxybenzoxazole, 6 -hydroxybenzoxazole), those of the naphthoxazole series (e.g. naphtho- [2,l-d]oxazole, naphtho[l,2-d]oxazole), those of the selenazole series (e.g. 4-methylselenazole, 4-phenylselenazole), those of the benzoselenazole series (e.g. benzoselenazole, S-chlorobenzoselenazole, S-methoxybenzoselenazole, 5 hydroxybenzoselenazole, 4,5,6,7 tetrahydrobenzoselenazole), those of the naphthoselenazole series (e.g. naphtho[2,1 d]selenazole, naphtho[l,2 d] selenazole), those of the 2-quinoline series (e.g. the quinoline, 3- methylquinoline, S-methylquinoline, 7-methylquinoline, '8- methylquinoline, 6-chloroquinoline, 8-chloroquinoline, 6- methoxyquinoline, 6 ethoxyquinoline, 6 hydroxyquinoline, 8-hydroxyquinoline, etc.), those of the pyridimine series, those of the quinoxaline series, those of the quinazoline series, those of the l-phthalazine series, those of the 2-pyridine series (e.g. pyridine, S-methylpyridine, 3- nitropyridine), those of the benzimidazole series (e.g. 1 ethylbenzimidazole, 1 phenylbenzimidazole, l-ethyl- 5,6-dichlorobenzimidazole, l-hydroxyethyl-5,6-dichlorobenzimidazole, l-ethyl 5 chlorobenzimidazole, l-ethyl- 5,6-dibromobenzimidazole, 1-ethyl-5-chloro-6-aminobenzimidazole, 1 ethyl 5 chloro-6-bromobenzimidazole, lethyl-S-phenylbenzimidazole, l-ethyl-S-fluorobenzimidazole, l-ethyl 5,6 difluorobenzimidazole, l-ethyl-S-cyanobenzimidazole, 1-( 8-acetoxy-ethyl)-5-cyanobenzimidazole, l-ethyl-S-chloro-6-cyanobenzimidazole, 1-ethyl-5-fluoro-6- cyanobenzimidazole, l-ethyl 5 acetylbenzimidazole, 1- ethyl-5-ch1oro-6-fluorobenzimidazole, 1 ethyl-S-carboxybenzimidazole, 1-ethy1-7-carboxybenzimidazole, l-ethyl- 5 carbethoxybenzimidazole, l-ethyl-7-carbethoxybenzimidazole, 1-ethyl-5-sulphamylbenzimidazole, or l-ethyl-S- N-ethylsulphamylbenzimidazole.

The following is a list of hydrazone compounds to most of which is referred in the examples.

S N 37) N (29) NHN=GH H 5 H N CH /N H N C a 30 N N NHN=OH l OZN The preparation of the hydrazone compounds 1, 2 and 5 is described by J. F. Golda-rd, F. Lions, J. Am. Chem.

IFIHLCH $06., 84, 2262-3 (1962).

The preparation of the hydrazone compound 23 is de- H scribed by F. Lions, K. V. Martin, J. Am. Chem. Soc., 80, N 3858-65 (1958). The preparation of the hydrazone compound 4 is as follows: (32) s NH N=OH 0.145 mole of the hydrazone compound 1 is dissolved in T 350 ccs. of boiling acetone. To the obtained solution 0.15 mole of zinc sulphate-7-water dissolved in 100 ccs. of Brwater 1s added whilst stlrrlng.

The solution is cooled. The precipitate formed is fil- (33) S CH3 tered off, once washed with cold water, twice with ethanol I and dried at 100 c. Analysis-Calculated (percent): C, 34.2; H, 3.37; N, 14.52; S, 8.31. Found (percent): C, 33.92; H, 3.70; N, 34 14.11; S, 8.87. HO Hydrazone compound 5 is prepared by heating compound 4 on an oil bath at 220 c. for 3 h. N The other hydrazone compounds are prepared according to the following general preparation method:

0.025 mole of hydrazino derivative dissolved or sus- (35) S NH-N=OH CH! pended in 25 ccs. of ethanol are mlxed w1th 0.025 mole l of aldehyde derivative dissolved in 25.ccs. of ethanol. 35 The reaction mixture is refluxed on a boiling water bath for 30 min. After cooling the formed precipitate is sucked (36) N N OE and washed with ethanol and dried. In most cases the NHN=OH obtained product is pure enough so that no further puri- (NHmGdCh fication is necessary. Only the compounds 20 and 22 are 40 recrystallized from ethylene glycol monomethyl ether.

In the following table the starting products, melting point and results of analysis of hydrazone compounds prepared according to the above general preparation method are listed.

Analysis Melting point, Cale Found, Number Hydl'azino derivative Aldehyde derivative 0. Elements percent percent 3 NHNH: 195 C 67.53 67.49 I H 4.45 4.25

CHO 1'1 6 S Same as above 266 O 59. 80 60. 02 H 3.92 4.16 HzN-N'H-fi! Ifil s 11. 46 11. 11

N--CCeH 7 S -do 210 c 64.25 64.18 H 4. 28 4.44 HzN-N'H-C (3H s 11. 42 11. 13

ILA-66H.

s d0 260 0 65.80 65.56 -NH H 4. 64 4. s2

)NHNH:

9 ..do 260 C 67.50 67.66 H 4.42 4.

NHNH2 Analysis Melting point, Calc., Found, Number Hydrazino derivative Aldehyde derivative C. Elements percent percent l N CH3 N/ OHO l NHNH:

11 Same as above 244 C 72.30 72. 07 H 4. 4. 64

\N/ CH 0 12 S Same as above 240 C 69.10 69. 46 HzN-NH- H 4. 24 4. 27 H 1 s 9. 70 1o. 00 N- Cells 13 8 260 C 53. 80 53. 96 HzN-NH C O O CzHs H 4. 83 5. 08 I I s 11. 04 10.83 NCH3 N OHO 14 Same as above 229 O 55. 25 55. 71 H 5. 26 5. 45 S 10.52 10. 61

CH3 N -CH O 15 .d0 257 C 60. 00 59. 83 H 4. 70 4. 86 S 9. 9. 19

CHO

16 S 260 C 46.70 46.56 -NHNH2 H 3. 00 3. 25 HO3S- s 19.18 19.38

N CH O 17 S Same as above 210 O 55.50 54. 92 H2NNH N H 3. 98 4. 01 I I s 19. 0o 19. 2s N s CHZQ 18 N 210 c 67.50 67. s w H 4. 42 4. as

CH O \N NHNHz 10 N 215 C 72. 30 72. 15 w H 4. 38 4. 48

N y CH O NH-NHz mN-NH-H u i N CH O N 02 21 Same as above 230 C 56.60 53. 98 H 3. 84 3. 86 S 9. 9. 59

. CH CHO 22 d0 260 C 60. 00 59. 63 H 3. 47 3. 51 S 8. 58 8. s5

N CH O 24 S Same as above 210 C 69. 80 67. 82 H2NNH H 4. 5. 62 i i s 9. 30 s. 46

Analysis POiIl a c. Foun Number Hydrazino derivative Aldehyde derivative 0. Elements percent; percen 25 S 233 C 70.80 71.09 HzN-NH C5H5 H 4. 50 4. 51 I I I S s. 97 9. 25 N--C0H5 N CHO 26 Same as above 246 C 71. 40 71.62 H 4.86 4. 98 S 8. 66 8. 82

CH1 N/ 0110 27 fin 240 C 74.00 .07 H 4. 43 4.51 S 7.87 8.00 N 2-0110 28 S 38 C 65.30 65.60 HzN-NH H 4. 76 4. 58 I I s 10. 39 10.88 v I CH0 29 Same as above 250 O 66. 20 66. 24 H 5.20 5.20 I s 10.40 10. 37 H C- N CHO 3o 260 C 54.37 54.40 OzN- H 3.73 3.35 I 0 13. 13.20 NHNHz GHQ I l N OCH CHO NHNH2 32 S 230 O 50.10 50.32 HzN-NH- H 3. 06 3. 15 I I I s 8.92 9.10 @431 GHQ 33 Same as above 250 C 51.50 51. 63 H 3.49 3.67 S 8.58 8.60

CH -CHO 34 260 C 55.70 55.90 H 3.18 3. 40 S 7.82 7.68

CHO

35 S 208 O 65. 30 65.56 H2NNH H 4. 76 5. 06 II I 5 10.00 11. 32 N Q 0115- CHO 37 N Same as above 174 0 64 63.96 \I H 5 34 5.30 NHNH:

A second class is represented by the following general Formula H:

wherein Z' has the same meaning as described for general Formula I.

As representatives of general Formula II are more particularly mentioned:

0 Compound 38:

Compound 39:

( NHN=CH N0, NI melting point 254 0.

Compound 40:

--NHN=CH NO: I l melting point 239 0. s

Compound 41:

N 0 -on,s- -NH=N-oH No I l l l NS melting point 222 C.

The hydrazone compounds according to the general Formula II are prepared according to the following general preparation method:

To a solution of 0.1 mole of a hydrazine compound corresponding to the following general formula:

wherein Z has the same meaning as described above, in 50 ccs. of dry ethanol a solution of 0.1 mole of S-nitrofuryl-2-carboxaldehyde in 50 ccs. of dry ethanol is added. A precipitate is formed. The reaction mixture is still 15 min. refluxed on a boiling water bath and cooled. The precipitate obtained is filtered off, successively washed with ethanol and ether and dried.

A third class which is especially valuable is represented by the following general Formula III:

wherein Z has the same meaning as described for general Formula I.

As representatives of general Formula IH are more particularly mentioned:

Compound 42:

N s Nn-N=oHUNoi compound corresponding to the following general formula:

melting point 260 0;

Compound 43:

melting point 260 C- wherein Z has the same meaning as described above, dissolved in 100 ccs. of ethanol, whereupon the reaction mixture is refluxed for 1 h. on a boiling water bath. After cooling the reaction mixture, the formed precipitate is sucked off, and successively washed with ethanol and ether.

A fourth class is represented by the following general Formula IV:

wherein Z has the same meaning as described for general Formula I.

As a representative of general Formula IV is more particularly mentioned: Compound 44 which compound can be prepared according to F. Lions, K. V. Martin, J. Am. Chem. Soc. (1958) 3860.

A fifth class is represented by the following general Formula V:

The compounds 45, 46 and 47 wherein R is respectively hydrogen, methoxy and .methylthio are prepared according to F. A. Snavely, W. S. Trahanovsky and F. H. Suydam, Inorg. Chem. 3 (1964) 123 A sixth class is represented by the following general Formula VI:

wherein each of R and R represents hydrogen, alkyl e.g. methyl or represent together the atoms necessary to close a homocyclic ring, e.g. a (CH;),; group, and

2' has the same meaning as described for general Formula I.

As representatives of general Formula VI are more particularly mentioned: Compound 48 melting point 210 0.

prepared according to F. Lions, K. V. Martin, I. Am. Chem. Soc. 80 (1958) 3858.

N 11 N-NHT O melting point 260 0.

prepared according to B. Chiswell, F. Lions, Inorg. Chem. 3 (11964) 490.

EA seventh class is represented by the following general Formula VII:

each of R and R represents alkyl e.g. methyl, aryl e.g. phenyl, or represent together the atoms necessary to close a homocyclic ring, and

Z has the same meaning as described for general Formula I.

As representatives of general Formula VH are more particularly mentioned:

Compound 50 Compound 51 melting point 178 C.

melting point 140 0.

Compound 52 melting point 169 C.

melting point 182 0.

Compound 54 Compound melting point 190 0: Compound 56:

melting point 222 C.

The compounds 50-55 are prepared according to B. Ohiswell, F. Lions, M. L. Tomlinson Inorg. Chem. 3 (1964) 492. Compound 56 is prepared analogously to the compounds 50-55.

An eight class is represented by the following general Formula VIII:

The compounds 57, 58, 59 and 60 wherein R is respectively hydrogen, methyl, carbethoxy and benzoyl are prepared according to B. Eistert, H. Selzer, Chem. Ber. 96 (1963) 314-319.

Further are mentioned chelating compounds for zinc ions containing an aromatic nucleus having in orthoposition to a hydroxyl group a CH=N group, a --CO--NH--N=CH group, a -N=N-aryl group, or a CH=N--N=CHaryl group and chelating compounds for zinc ions containing in orthoposition to a carboxyl group an azo group.

Examples of further compounds useful herein are as follows:

Compound 61 N\C @J lie melting point 260 C.- which is prepared as follows:

To 0.1 mole of 2(o-aminophenyl)benzimidazole (Ber. 32, 1465) dissolved in 100 ccs. of ethanol 0.1 mole of salicyl aldehyde is added. The reaction mixture is refluxed for 2 h. on a boiling water bath. The precipitate formed is sucked off and washed with ether. Melting point 260 C. and

Compound 62 OH 11 0 I Melting point 213 C:

The sensitizing compounds are preferably used in dissolved form to sensitize the inorganic photoconductor which is normally used in dispersed form in a solution or dispersion of a binder. They may be mixed beforehand, for example dissolved in dimethylformamide with the photo conductor e.g. zinc oxide. The sensitizing compound is then adsorbed on the photoconductor grains and can complex metal ions provided by the photoconductor. The sensitized photoconductor thus treated is then mixed with a suitable binder, whereupon the whole composition can be coated on a suitable base material.

The sensitizing compounds may also be used in complexed form as can be seen e.g. in Example 2. Thus it is not absolutely necessary to treat the photoconductive substances with the sensitizing compounds in non-complexed form, although the sensitizing treatment with the compounds in non-complexed form is preferred.

The sensitizing compounds used in the present invention are preferably applied in combination with an acid to produce metal ions; preferably the acid compounds described in Belgian patent specification 612,102 filed Dec. 29, 1961 by Ge'vaert Photo-Producten N.V. which increases the dark resistivity of photoconductive zinc oxide are used. Of course the spectral sensitivity of photoconductive recording layers according to the present invention may be further modified by sensitizing compounds other than those described herein.

Combinations with other optical sensitizing compounds may be applied in order to make the recording layer sensitive for the whole range of the visible spectrum, so that the recording layer becomes suitable for multicolour reproduction.

The quantitative ratio of photoconductor to sensitizing agent may vary within wide limits and depends on the effect desired; the amount of sensitizing agent may for instance vary between 0.001 and 0.5 percent based on the weight of photoconductor. Representatives of sensitizing compounds which are very active can be chosen in Table 2 of Example 3 given further on. Most of these compounds sensitize in the range of 440 to 515 nm.

In a well known type of xerography the photoconductive substances are used in combination with a binding agent the electric specific resistance of which is preferably at least ohm cm.

The quantitative ratio of photoconductive substance to binding agent may vary within wide limits. Preferably the ratio of binding agent to photoconductor is between 1:1 to 1:10 parts by weight. The thickness of the photoconductive layer may be chosen between wide limits according to the requirements of each case. Good recording and reproduction results are attained with electrophotographic layers of a thickness between 1 and 20g, and preferably between 3 and 1011.. Too thin layers possess an insufficient insulating power whereas too thick layers require long exposure times.

Suitable binding agents for photoconductive substances of the inorganic type are e.g. described in Belgian patent specifications 612,102 filed Dec. 29, 1961 and 604,126 filed May 24, 1961 both by Gevaert Photo-Producten N.V. The photoconductive recording layers containing photoconductive substances sensitized according to the present invention may further contain photoconductive substances, that cannot be sensitized with the sensitizing compounds corresponding to the above cited general formula e.g. organic monomeric photoconductors described in Belgian patent specifications 585,507 filed Dec. 10, 1959, 585,555 filed Dec. 11, 1959, 587,301 filed Feb. 5, 1960, 585,450 filed Dec. 9, 1959, 587,794 filed Feb. 19, 1960, 589,239 filed Mar. 31, 1960, 594,974 filed Sept. 13, 1960, 595,696 filed Oct. 4, 1960, 597,616 filed Nov. 30, 1960 and 625,683 filed Dec. 5, 1962 all by Gevaert Photo-Producten N.V., and polymeric photoconductors described in Belgian patent specifications 599,627 filed Jan. 30, 1961, 588,049 filed Feb. 26, 1960, 588,048 filed Feb. 26, 1960 and 588,050 filed Feb. 26, 1960 all by Gevaert Photo-Producten N.V., as well as sensitizers for these photoconductive substances. Furthermore in the recording layer additives known in coating techniques may be used e.g. pigments (see e.g. Belgian patent specification 609,056 filed Oct. 12, 1961 by Gevaert Photo-Producten N.V.), compounds that influence the gloss and/or the viscosity, compounds that counteract ageing and/or oxidation of the layers, compounds that influence the thermal stability of the layers. When selecting any additives preference is given to those that least of all reduce the dark resistivity of the photoconductive layer.

The photoconductive recording layers or sheets sensitized according to the present invention can be prepared by any of the processes known therefor. Thus, the photoconductor-binder composition with a suitable solvent or dispersing liquid for the binder may be coated on a sup port by a known coating technique e.g. by spraying, by whirling, by dip-coating, or by a coating technique wherein use is made of a doctor blade. The supports or base materials are chosen in view of the particular exposing, recording, developing and/or transfer technique wherein the recording material is to be used.

Preferably for xerographic purposes the support has an electric volume resistivity considerably lower than that of the recording layer. Suitable supports are e.g. described in Belgian patent specifications 602,794 filed Apr. 20, 1961, 612,102 filed Dec. 29, 1961 and 610,060 filed Nov. 8, 1961 all by Gevaert Photo-Producten N.V. and the US. patent specification 3,008,825 filed Nov. 20, 1957 by W. G. Van Dorn and O. A. Ullbrich.

The photoconductive layer of an electrophotographic material optically sensitized according to the present invention can be made sensitive for recording purposes by electrically charging according to known methods. The material can, however, also be used in recording techniques, wherein the exposure step precedes charging; for such a technique we refer e.g. to Belgian patent specification 625,335 filed Nov. 27, 1962 by Gevaert Photo- Producten N.V.

The following examples illustrate the present invention without, however, limiting the present invention thereto.

EXAMPLE 1 120 g. of copoly(vinyl acetate/ vinyl laurate) (/20) are dissolved in 500 cos. of toluol. To this solution are added 20 cos. of a 10% solution in ethanol of monooctylphosphate and 300 g. of photoconductive zinc oxide (prepared according to the French process) which has been dried for 30 min. on C.

After grinding the whole composition for 15 h. in a ball mill 20 cos. of a 5% solution in ethanol of succinic acid are added and 6 cos. of a 10% solution in dimethyl formamide of one of the hydrazone compounds indicated hereinafter in the table. The dispersion obtained is coated on a glassine paper base which does not absorb toluol. The dried layer weighs 25 g. per sq. m.

A series of recording materials are prepared in this way; among this series one material does not contain sensitizing compound and each of the other materials contains a diiferent sensitizing compound as listed hereinafter in the table.

The different recording materials obtained are simultaneously charged with a corona discharging apparatus having a potential difference between the ground and the wires of 6000 v., the wires being connected to the negative pole of a direct current source. The charged materials are exposed under the same conditions with incandescent light bulbs through a grey wedge having a constant 0.1.

The charge images obtained are simultaneously developed with a resin powder toner that contains iron filings as carrier. The toner is fixed by heating.

The sensitometric results presented in the following Table 1 are relative values; the non-sensitized material is given the value 1.

TAB LE 1 TABLE 2 List of the sen- Maximum Percent by sitizing eom Relative spectral weight of pound of the total sensensitivity, sensitizing list given above sitivity 11m. compound 5 Number relative to Maximum 1 of the the amount Relative spectral 5 445 sensitizing of zinc total sensitivity, 8 505 compound oxide sensitivity nm. 10 445-505 12 505 1 10 505 0.5 20 445 0.5 64 445-505 10 0. 05 16 445-505 0. 5 20 445 0.5 16 505 0.5 16 475 0.2 20 505 0.5 12 515 0.5 20 505 15 0.5 16 515 0. 5 20 5 555 EXAMPLE 2 0.5 50 475 v 0.5 16 445 250 cos. of a 20% solut1on 1n toluol of silicon resin, 7S0 ccs. of toluol, 20 cos. of a 10% solution in ethanol of 5 10 505 monobutylphosphate, 300 g. of photoconductive zinc 20 8.? 3 505-212 oxide (prepared according to the French process) and 64 505 6 g. of the sensitizing compound number 4 are mixed for 3.? 1 6 2 1 16 h. in a ball mill. The further processing steps occur 40 515 as described in Example 1. The sensitized material has a 232 general sensitivity which is 4 times as high as the sensi- 16 515 tivity of the corresponding non-sensitized material. 8-; $2 282 0:2 25 EXAMPLE 3 0.5 8 0.05 6 505-515 0.5 6 640 g. of copoly(vmy1 acetate/vinyl laurate) (80 /20) 05 1 1 are dissolved in 8 litres of toluol. To this solution are add- 64 605 0.05 40 515 ed and mixed therewith m a ball-mill 64 cos. of a 10% 0.2 8 605 solution in ethanol of monotn'decylphosphate and 2.4 kg. 2 g of photoconductive zinc oxide (prepared according to the .2 23 605 French process). 0:? 61:11:11:

To the dispersion obtined 320 cos. of a 5% solution in ethanol of succinic acid are added as well as an amount EXAMPLE 4 a g 4 as hsted m 12 3 3 2; In the following table the composition of different a urt er processmg (,mcurs escn e m 40 photoconductive recording layers is illustrated. Said layers lmple wlth a P? P recordmg mammals each are coated on a glassine paper. The relative sensitivity 111g f dlfferent seflsltlzlng Compound and one matenal c011 values are calculated by comparing the sensitized matetalmng no sensltlzlllg p rials With the same but non-sensitized material the sensi- The sensltemetrle results represented 1n the fellowmg tivity of Which is given the relative value 1. The coating table 2 are also relative values, the non-sensitized material 4? and further processing steps of the recording layers are is given the value 1. 0 carried out in the same way as illustrated in Example 1.

Percent by weight of monobutyl Ratio by Percent by phosphate weight of weight of senrelative to the binding agent sitizing comamount of to photocon- Solvent for Number of the pound relative Maximum photoconducductive zine the binding sensitizing to the amount Relative spectral sensi. Binding agent tive zinc oxide oxide agent compound of zinc oxide sensitivity tivity, nm

0.6 6 0. 2 3 445 Polyvinyl butyral. 0. 6 2:20 Ethanol 7 0. 2 8 505 0.6 s 0.2 4 475 Oopolyster of 2,2-(4,4-dihydroxy- 1 4:15 Methylene 11 0.2 6 505 diphenyl)-propane, isophthalic acid 1 chloride. 0 0. 2 12 505 and terephthalic acid (/25). G op oly (methyl methacrylate/n-butyl- 0. 6 10: 30 Acetone 10 0. 1 4 475 methacrylate) (60/40).

Polycarbonate of 2,2-(4,4-dihydroxy- 0. 6 Methylene 8 0. 2 12 505 diphenyD-propane. 0. 6 4: 15 chloride. 9 0. 2 3 475 0.6 11 0.2 3 505 0.6 9 0.2 3 505 Aliphatic keton resin 0. 6 6:15 Ethanol 4 2 16 555 0.6 3 2 16 505 Copoly(vinylchloride/vinylacetatel- 4. 4:15 Acetone 11 0. 2 6 475 vinylalcohol) (91/3/6) C opoly (n-butyl rnethacrylatel- 10 O. 2 4 475 isobutylmethacrylate) (40/60) 4: 15 Toluol 11 0. 2 2 5 505 9 0.2 10 505515 Copoly(vlnyl acetatel-vinyl stearate) 0. 6 Ethylene 10 0. 2 20 475 (/15). 0. 6 4: 22. 5 glycol mono 11 0. 2 32 505 0. 6 mlethyl e 0. 2 16 505 ether. Copoly(n-butyl methacrylatel-iso- 0.6 2 2 16 575 butylmethacrylate) 40/60). 0.6 4:15 T011101 3 0.5 s 445-505 19 EXAMPLE To 1 litre of an 8% solution in toluol of coply(vinyl acetate/ vinyl laurate) 80/20) added whilst stirring:

8 ccs. of a 10% solution in ethanol of monobutyl phosphate 300 g. of zinc oxide (prepared according to the French process).

The mixture is ground for 16 h. in a ball mill whereupon 40 ccs. of a 5% solution in ethanol of succinic acid are added. The whole is stirred for another 4 hours and then the dispersion obtained is intimately mixed with the following mixture of optical sensitizing agent:

ccs. of a 10% solution in dimethylformamide of hydrazone compound 9 and 3.3 ccs. of 1% solution in dimethyl formamide of Eriocyanine A (Acid Blue 34, Cl. 42,561).

The sensitized composition is coated onto a glassine paper support at a ratio of g. of solid dry substance per sq. m.

The recording layer is successively but separately exposed to a positive colour transparency through a blue, a green and a red filter while before each exposure a uniform electrostatic negative charge is applied to the recording layer by corona discharge. The charge images respectively obtained are developed with a developing pigment dispersed in an insulating liquid (hexane) which pigment has a colour complementary to the colour of the filter used at the exposure. A positive copy of the colour transparency is obtained in this way.

EXAMPLE 6 Example 2 is repeated but compound 4 is replaced in the same concentration by compound 44.

The sensitized material has a general sensitivity which is 2.5 times as high as the sensitivity of the corresponding non-sensitized material.

EXAMPLE 7 Example 3 is repeated but using the compounds listed in the table with their sensitometric results.

Percent by weight of sensitizing compound relative to Maximum Number of the amount Relative spectral the sensitizing of zinc total sensitivity, compound oxide sensitivity nm.

What is claimed is:

1. A photoconductive recording element comprising a photoconductive layer consisting essentially of photoconductive zinc oxide as the essential photoconductor thereof and a sensitizing amount of a colored chelate complex of an organic chelating agent with ions of said photoconductive zinc oxide, said chelate complex imparting increased light sensitivity to said photoconductive layer, said organic complexing agent having the following general formula:

wherein:

each of Z and Z' represents the necessary atoms for completing a fiveor six-membered ring, and

R represents a hydrogen atom or an alkyl radical, said layer being free of sensitizing agents for said photoconductive compound other than said chelate complex.

2. A photoconductive recording element comprising a photoconductive layer consisting essentially of photoconductive zinc oxide as the essential photoconductor thereof and a sensitizing amount of a colored chelate complex of an organic chelating agent with ions of said photoconductive zinc oxide, said chelate complex imparting increased light sensitivity to said photoconductive layer, said organic complexing agent having the following general formula:

wherein Z represents the atoms necessary to complete a fiveor six-membered ring, said layer being free of sensitizing agents for said photoconductive compound other than said chelate complex.

3. A photoconductive recording element comprising a photoconductive layer consisting essentially of photoconductive zinc oxide as the essential photoconductor thereof and a sensitizing amount of a colored chelate complex of an organic chelating agent with ions of said photoconductive zinc oxide, said chelate complex imparting increased light sensitivity to said photoconductive layer, said organic complexing agent having the following general formula:

wherein Z represents the atoms necessary to complete a fiveor six-membered ring, said layer being free of sensitizing agents for said photoconductive compound other than said chelate complex.

4. A photoconductive recording element comprising a photoconductive layer consisting essentially of photoconductive zinc oxide as the essential photoconductor thereof and a sensitizing amount of a colored chelate complex of an organic chelating agent with ions of said photoconductive zinc oxide, said chelate complex imparting increased light sensitivity to said photoconductive layer, said organic complexing agent having the following general formula:

wherein:

each of R and R represents hydrogen, or alkyl, or represent together the atoms necessary to close a homocyclic ring, and Z represents the atoms necessary to close a fiveor six-membered ring,

21 22 said layer being free of sensitizing agents for said photowherein: conductive compound other than said chelate complex. each of R and R represents alkyl or aryl, and

6. A photoconductive recording element comprising a Z represents the atoms necessary to close a fiveor photoconductive layer consisting essentially of photoconsix-membered ring,

ductive zinc oxide as the essential photoconductor thereof 5 said layer being free of sensitizing agents for said photoand a sensitizing amount of a colored chelate complex conductive compound other than said chelate complex. of an organic chelating agent with ions of said photoconductive zinc oxide, said chelate complex imparting in- References Cited creased light sensitivity to said photoconductive layer, UNITED STATES PATENTS gfgfi g agent havmg the 10 3,121,006 2/1964 Middleton et al 961.5 3,315,599 4/1967 Lind 96-1X R4\ /N\ CHARLES E. VAN HORN, Primary Examiner F NH 15 US. 01. X.R. 

